This invention relates to a method of measuring bulk residual stress by a semi-nondestructive technique.
Residual stress is also known as internal stress and is defined as a stress system within a solid that is not dependent on external forces. The two key residual stress techniques in current use are the stress relief methods and the x-ray method. The first as traditionally practiced, such as by drilling or machining a hole in a specimen to relieve the stresses, is destructive. Efforts to measure residual stress nondestructively have met with little success except for the use of x-rays, but this is only applicable to within one-half mil of the surface and is not adaptable to measuring residual stress on the inside surface of a pipe or other internal surface.
A related application is Ser. No. 038,069 filed on May 11, 1979 by J. R. M. Viertl and M. G. Jones, "Semi-Nondestructive Residual Stress Measurement", assigned to the same assignee. In the foregoing surface strain is measured dynamically before the heat of a locally melted region diffuses under the strain gage and results in thermal stress. By semi-nondestructive it is meant that the damage to the part is so small that the part tested is not impaired for further service.